Title: Defect phase diagram for doping of Ga 2O 3

For the case of n-type doping of β-Ga 2O 3 by group 14 dopants (C, Si, Ge, Sn), a defect phase diagram is constructed from defect equilibria calculated over a range of temperatures (T), O partial pressures (pO 2), and dopant concentrations. The underlying defect levels and formation energies are determined from first-principles supercell calculations with GW bandgap corrections. Only Si is found to be a truly shallow donor, C is a deep DX-like (lattice relaxed donor) center, and Ge and Sn have defect levels close to the conduction band minimum. The thermodynamic modeling includes the effect of association of dopant-defect pairs and complexes, which causes the net doping to decline when exceeding a certain optimal dopant concentration. The optimal doping levels are surprisingly low, between about 0.01% and 1% of cation substitution, depending on the (T, pO 2) conditions. Considering further the stability constraints due to sublimation of molecular Ga 2O, specific predictions of optimized pO 2 and Si dopant concentrations are given. To conclude, the incomplete passivation of dopant-defect complexes in β-Ga 2O 3 suggests a design rule for metastable doping above the solubility limit.

@article{osti_1435905,
title = {Defect phase diagram for doping of Ga2O3},
author = {Lany, Stephan},
abstractNote = {For the case of n-type doping of β-Ga2O3 by group 14 dopants (C, Si, Ge, Sn), a defect phase diagram is constructed from defect equilibria calculated over a range of temperatures (T), O partial pressures (pO2), and dopant concentrations. The underlying defect levels and formation energies are determined from first-principles supercell calculations with GW bandgap corrections. Only Si is found to be a truly shallow donor, C is a deep DX-like (lattice relaxed donor) center, and Ge and Sn have defect levels close to the conduction band minimum. The thermodynamic modeling includes the effect of association of dopant-defect pairs and complexes, which causes the net doping to decline when exceeding a certain optimal dopant concentration. The optimal doping levels are surprisingly low, between about 0.01% and 1% of cation substitution, depending on the (T, pO2) conditions. Considering further the stability constraints due to sublimation of molecular Ga2O, specific predictions of optimized pO2 and Si dopant concentrations are given. To conclude, the incomplete passivation of dopant-defect complexes in β-Ga2O3 suggests a design rule for metastable doping above the solubility limit.},
doi = {10.1063/1.5019938},
journal = {APL Materials},
number = 4,
volume = 6,
place = {United States},
year = {2018},
month = {4}
}

A description and structural study of four quaternary compounds is furnished: (LaO)/sub 4/Ga/sub 1,33/S/sub 4/ and ..cap alpha..-LaGaS/sub 2/O have sheet structures, formed by (LaO) sheets and gallium sulfide sheets. La/sub 3/GaS/sub 5/O has a ribbon structure, formed by (La/sub 2/O) ribbons inside a LaGaS/sub 5/ sulfide skeleton. In the three preceding compounds, oxygen is bound only to lanthanum, and gallium is bound only to sulfur. No such bond selectivity occurs in ..beta..-LaGaS/sub 2/O and La/sub 3,33/Ga/sub 6/S/sub 12/O/sub 2/. An interpretation of the structural characteristics of the Ga - (O,S) arrangements is presented in relation to the composition. Amore » partial description of the phase diagram (for O/O + S) < 0.50) is presented. The La/sub 2/O/sub 2/S-Ga/sub 2/S/sub 3/ system is quasi-binary. The La/sub 2/O/sub 3/-Ga/sub 2/S/sub 3/ system is a section in the ternary system, involving three-phase equilibria. A description of the eutectic valleys and of the ternary invariants is furnished. 23 references, 8 figures, 5 tables.« less

Structures of compounds in the Cu{sub 2}Se-In{sub 2}Se{sub 3}-Ga{sub 2}Se{sub 3} system have been investigated through X-ray diffraction. Single crystal structure studies for the so-called stoichiometric compounds Cu(In,Ga)Se{sub 2} (CIGSe) confirm that the chalcopyrite structure (space group I4-bar 2d) is very flexible and can adapt itself to the substitution of Ga for In. On the other hand a structure modification is evidenced in the Cu{sub 1-z}(In{sub 0.5}Ga{sub 0.5}){sub 1+z/3}Se{sub 2} series when the copper vacancy ratio (z) increases; the chalcopyrite structure turns to a modified-stannite structure (I4-bar 2m) when z{>=}0.26. There is a continuous evolution of the structure from Cu{submore » 0.74}(In{sub 0.5}Ga{sub 0.5}){sub 1.09}Se{sub 2} to Cu{sub 0.25}(In{sub 0.5}Ga{sub 0.5}){sub 1.25}Se{sub 2} ((i.e. Cu(In{sub 0.5}Ga{sub 0.5}){sub 5}Se{sub 8}), including Cu{sub 0.4}(In{sub 0.5}Ga{sub 0.5}){sub 1.2}Se{sub 2} (i.e. Cu(In{sub 0.5}Ga{sub 0.5}){sub 3}Se{sub 5}). From this single crystal structural investigation, it is definitively clear that no ordered vacancy compound exists in that series. X-ray photoemission spectroscopy study shows for the first time that the surface of powdered Cu{sub 1-z}(In{sub 0.5}Ga{sub 0.5}){sub 1+z/3}Se{sub 2} compounds (z{ne}0) is more copper-poor than the bulk. The same result has often been observed on CIGSe thin films material for photovoltaic applications. In addition, optical band gaps of these non-stoichiometric compounds increase from 1.2 to 1.4 eV when z varies from 0 to 0.75. - Abstract: Pseudo-ternary diagram in the Cu{sub 2}Se-In{sub 2}Se{sub 3}-Ga{sub 2}Se{sub 3} system showing the composition of all the synthesized compounds. The crystal structure of the compounds corresponding to red circles are presented in this study.« less